Cascade geothermal drilling/corehole N-1

Abstract

Two core holes have been completed on the flanks of Newberry Volcano, Oregon. Core hole GEO N-1 has a heat flow of 180 mWm-2 reflecting subsurface temperature sufficient for commerical exploitation of geothermally generated electricity. GEO N-3, which has a heat flow of 86 mWm-2, is less encouraging. Considerable emphasis has been placed on the ''rain curtain'' effect with the hope that a detailed discussion of this phenomenon at two distinct localities will lead to a better understanding of the physical processes in operation. Core hole GEO N-1 was cored to a depth of 1387 m at a site located 9.3 km south of the center of the volcano. Core hole GEO N-3 was cored to a depth of 1220 m at a site located 12.6 km north of the center of the volcano. Both core holes penetrated interbedded pyroclastic lava flows and lithic tuffs ranging in composition from basalt to rhyolite with basaltic andesite being the most common rock type. Potassium-argon age dates range up to 2 Ma. Difficult drilling conditions were encountered in both core holes at depths near the regional water table. Additionally, both core holes penetrate three distinct thermal regimes (isothermal (the rain curtain), transition, andmore » conductive) each having its own unique features based on geophysical logs, fluid geochemistry, age dates, and rock alteration. Smectite alteration, which seems to control the results of surface geoelectrical studies, begins in the isothermal regime close to and perhaps associated with the regional water table. 28 refs., 15 figs., 2 tabs.« less